Method for stripping color from keratinous material



FIP83D9 X R 2 9 8 5 1 4 9 6 Patented Aug. 3, 1954 i Retreats METHOD FOR ,STRIPPIN G COLOR FROM KERATINOUS MATERIAL Milton Harris, Bethesda, and Alfred E Brown, Princ Geo ges County, Md, assignors, by 3136. 2 aqig lpienta to Harris ltescar'ch Lab- QFMQ i Q 111% efi fiqifl D. 0., a corporat ae D ware N 0 Drawing. Application May :22, 19 51, TSeriail'No. 227,754

10 Qlaims.

The p esent e at is the eater es Q olar from ls atieqr materi l su a weal. air in? the like Th se mat ria s ar charac erize "b the esas ther i 01- keratin a f bl u pmtai l ins a no acids n ludi g cysi a Th ie .0 aci s re Joined t ethe b p tide linka s is form pr tein hain and the resu tin c a are ra s l nk d y he disables r u -57 9 cystine.

In re ar n W99 pr clude uch a ,shq si c ip ing ra s an the ike or reara sss e it i n essa t em ve th Elsi 9 9.01 rom the wool. A widely used practice is to strip colors from wool in acidic media with sodium or zinc formaldehyde sulfoxylate. This treatment adversely affects the mechanical as well as the chemical properties of the wool, even when the processing conditions are carefully controlled. Both the wettensile strength and the dry tensile strength are decreased, especially the former, and

increased. In some cases a second strip is essential to remove the color and in these cases chem;

ical damage to the wool is further increased.

Wool products stripped by these conventional pro cedures also show an increased susceptibility to damage when treated under oxidizing, reducing,

acid or alkaline conditions in subsequent process;

Another, and preferred, process is to subjeot the wool to the action of a reducing agent' for keratin in the presence of an alkylene dihalide, as described in our prior Patent No. 2,508,714

dated May 23, 1950. The present invention is an improvement on the stripping process described in this prior patent. i

t is an object of the invention to provide an improved process for stripping colorfrom wool and like materials. Another object is to provide a process for stripping color from wool which will yield stripped wool materials having improved resistance to attack by oxidizing agents, reducing agents, acids and alkalis, substantially unimpaired physical properties, and a lighter coor than can-be obtained with known procsses. l l he Qb is 9 Provide wim r ved T5 9 Stripping 9 9 bm e er -dyad WQTQ ;B t e mass at the present .iav niiq i is 2 possible to strip color from wool without sub- 'stantial impairment of the mechanical properties of the wool and with improvement in its resistance to attack by oxidizing, reducing, acid and alkaline agents, as'with the process of our said prior patent, and, in addition, it is possible to produce lighter colored products, .especially from certain chrome-dyedvwool stocks, than can be produced with prior processes, without substantially altering the properties of the stripped material. this respect, the process is particularly usefulin many applications where very light stripped products are required, such as materials which are subsequently to be used for pastel shade dyeing.

'In accordance with the invention the keratinqs materia a as dyed r991 S e ted t t stionofa redu in a a en and i th e bat fillbi Qfi-td 9 the alie p ne ent or s di W wi l er to t is oxali a "d reat s p t atm nt ilh described treatea esm .asentasda krls eei e ds W1- sli nse eferr d toil 2? rs $1 3 5?! men and th es r ed final ac str p s c nd sta e tr atment I i see sis si he pre rse e sts ptimal and s ferred w t ph m rdrsd mat als 91. ar in which this pretheatmeht step is omitted is applicable to dyed keratinous material whether chrome-dyed or not.

The action of reducing agents .on :keratinous material ordinarily results in rupture of disulfide linkagesand damage .to the fiber. In our process, however, inwhich an alkylene dihalide is present with the reducing agent during our first stage step, the linkages ruptured by the reducingagent are immediately .rebuilt with the formation .of new stable linkages. We provide a highlyeilective, commercially practical process for .producing stripped modified wool materials, particularly from chrome-dyed stocks, .of :lighter or different colorshades thancanbeproduced by other processes without adversely'afiecting the physical properties of the wool.

The nvee iqn i il i st eiss :PY he iel ewia example of procedures by which it may be put into practice. It will be understood that the described pretreatment with oxalic acid and sulfuric acid (and the subsequent neutralization with alkali) may be omitted, especially if the dyed wool has not been chrome-dyed, as was disclosed in our prior application Serial No. 160,582, filed May 6, 1950.

Example I to 90 C. The wool is so treated for 15 minutes,

the bath is then dropped, and the stock is rinsed. Then hot water is admitted to about the same volume a before, and 0.2 part of zinc sulfoxylate formaldehyde is added along with 0.15 part of 90% formic acid. The wool is then treated at the boil for about 15 minutes. The bath is then dropped, and the wool is rinsed. It is often advantageous to have about 0.1% sulfuric acid in the rinse liquor. A stripped sample of very light color is produced. The strength of the stripped wool is very similar to that of the untreated material.

Example II Chrome dyed wool constituting parts is immersed in a bath comprising 0.5 part oxalic acid and 0.5 part sulfuric acid dissolved in 300 parts of water. The bath is heated at the boil for minutes. It is then neutralized with alkali and 3 parts of borax are dissolved in the bath. Then 0.5 part of 1,2-dibromoethane containing 0.025 part of oleic acid (red oil) is added to the solution. With normal cooling the temperature of the bath at this time is about 60 C. Sodium hydrosulfite, 0.3 part, is added and the temperature is raised to 90 C. The Wool is so treated for 15 minutes, the bath is then dropped, and the stock is rinsed. Hot water is then admitted to about the same volume as before, 0.3 part of zinc hydrosulfite is added and the temperature is raised to 90 C. The bath is kept at this temperature for an additional 15 minutes, after which the bath is drawn oil, and the wool is rinsed. A stripped wool of light shade and desirable physical properties is so produced.

Example III Chrome dyed wool constituting 10 parts is immersed in a bath comprising 0.5 part oxalic acid, 0.2 part sulfuric acid and 0.01 part of the tetrasodium salt of ethylenediaminetetraacetic acid, known commercially under the trade name Versene, all dissolved in 300 parts of water. The bath is heated at the boil for 15 minutes. The bath is then neutralized with alkali and 3 parts of borax are dissolved in it. Then 0.5 part of 1,2-dibromoethane containing 0.025 part of oleic acid (red oil) is added to the solution. With normal cooling the temperature at this time is about 60 C. Sodium hydrosulfite, 0.3 part, is added and the temperature is raised to 90 C. The Wool is so treated for 15 minutes, and the bath is then dropped and the stock is rinsed. Hot Water is then admitted to about the same volume as before, and 0.2 part of zinc sulfoxylate formaldehyde is added along with 0.15 part of formic acid. The wool is then treated at the boil for about 15 minutes. The bath is dropped and the wool is rinsed. A stripped sample of very light color is produced. The strength of the stripped sample is very similar to that of the untreated wool. 1

Example IV Chrome dyed wool constituting 10 parts is immersed in a bath comprising 02 part oxalic acid and 0.2 part sulfuric acid dissolved in 300 parts of water. The bath is heated at the boil for 30 minutes. The bath is then neutralized with alkali and 3 parts of borax are dissolved in it. Then 0.5 part of 1,2-dibromoethane containing 0.025 part of oleic acid (red oil) is added to the solution. With normal cooling the temperature at this time is about 60 C. Sodium hydrosulfite, 0.3 part, is added and the temperature is raised to 90 C. The wool is so treated for 15 minutes, the bath is then dropped, and the stock is rinsed. Hot water is then admitted to about the same volume as before, and 0.2 part of zinc sulfoxylate formaldehyde is added along with 0.15 part of 90% formic acid. The wool is then treated at the boil for about 15 minutes. The bath is then dropped, and the wool is rinsed. It is often advantageous to have about 0.1% sulfuric acid in the rinse liquor. A stripped sample of very light color is produced. The strength of the stripped wool is very similar to that of the untreated material.

Example V Chrome dyed wool constituting 10 part is immersed in a bath comprising 0.3 part oxalic acid and 0.1 part sulfuric acid dissolved in 300 parts of water. The bath is heated at the boil for 30 minutes. The bath is then neutralized with alkali and 3 parts of borax are dissolved in it. Then 0.8 part of 1,2-dibromopropane containing 0.025 part of oleic acid (red oil) is added to the solution. With normal cooling the temperature at this time is about 60 C. Then 0.3 part of sodium hydrosulfite is added to the bath, and the temperature is raised to 90 C. The Wool is treated for 15 minutes, and the bath is then dropped and the stock is rinsed. Hot water is then admitted to about the same volume as before, and 0.2 part of zinc sulfoxylate formaldehyde is added along with 0.15 part of 90% formic acid and the temperature is raised to the boil. The bath is kept at the boil for about 15 minutes, then drawn off and the wool is rinsed as in Example I. A stripped stock of desirable color and mechanical properties is obtained in this manner.

Our pre-treatment step, with an oxalic and sulfuric acid bath, is conveniently carried out in conventional mil-l equipment. If desired the bath may be dropped at the end of this stage, i. e., before the treatment with reducing agent and alkylene dihalide, but this is an extra step and it is more convenient to adjust the alkalinity Without dropping the bath.

Removal of the wool from the bath at the end of the first stage treatment, as in the foregoing examples, is desirable inasmuch as it assures that dyestufi stripped by the initial stabilization and stripping procedure is removed from the sphere of the reaction. However, it is also feasible to perform the second stage treatment in the reaction bath in which the pretreatment and first stage treatment were carried out. In this case the second stripping compound is added directly to the reaction bath immediately after the first stage treatment has progressed to the desired degree. compound desired during the second stage, such as an acid for increasing the stripping action when zinc sulfoxylate formaldehyde is employed as the second stripping compound. With zinc sulfoxylate formaldehyde, and allied sulfoxylates, which, we have found, give the best color removal, the pH should be in the range 3 to 4.5, and preferably in the range 3.2 to 3.7. The indicated pI-I can be obtained by addition of an appropriate acid, e. g., formic, acetic or sulfuric acid. When zinc hydrosulfite is used as the second stripping compound the pH is preferably in the range 5.5 to 7.0. The zinc hydrosulfite itself gives a pH value in this range and no other addition is necessary.

The concentration of oxalic acid in the first stage treatment can be varied widely without any deleterious eifect. Amounts ranging from about 1% to about on the weight of the wool are preferred with about 3% on the weight of the wool being generally aplicable. No advantage in color removal is gained by further increase in concentration of oxalic acid.

Acidic solutions of oxalic acid are preferred to neutral or alkaline solutions. Although oxalic acid alone may be used, more desirable results are obtained when a strong acid is also present. Thus, 2 to 5% of sulfuric acid on the weight of the wool is found suitable. In general, the pH of such solutions will be in the range of 1.5 to 2.5. Although other acids may be used, sulfuric acid is very satisfactory.

In some cases, the addition of small amounts of a sequestering agent, such as the tetrasodium. salt of ethylenediaminetetraacetic acid, to the oxalic acid and sulfuric acid bath aids in the ultimate color removal, and such agents may also be used.

Examples of reducing agents suitable for use in the first stage of our process are the hydrosulfites, formamidine sulfinic acid, the various sulfoxylate-formaldehyde compounds, e. g., sodium sulfoxylate formaldehyde, and the like. Other reducing agents may be used, but they should be of a. type which does not react with the alkylating agent (as would thiol compounds such, for example, as thioglycolic acid and salts thereof, monothioethylene glycol, and other mercaptans), since otherwise. the two components of the solution would be exhausted by reaction with each other and would not be available for reaction with the wool.

The stripping compound employed in the second stage of our process may be any material which removes color from wool. Since the wool is stabilized by the first stage treatment, improved stripping is now obtained with little or no change in properties of the keratinous material. Typical of compounds which give excellent results in producing light color shades are the strong stripping agents such as zinc hydrosulfite and zinc sulfoxylate formaldehyde. Desirably an organic or inorganic acid is added along with the zinc sulfoxylate formaldehyde, as indicated above.

The choice of reducing agents will depend on the cost and the quality of the strip and will also depend upon the type of dye or color to be removed. Small scale trials will quickly indicate the best set of conditions to use for any given batch of goods.

In our process, a preliminary scouring with At the same time is added any other ammonia is not necessary, as compared with present commercial stripping processes carried out on the acid side. This is an advantage from the standpoint of saving of processing time and costs; However, in some cases a better strip can be obtained by first giving the wool an ammonia scour, especially with greasy materials. Such a scour can be done using 2% to 5% of ammonia, on the weight of the wool for 30 minutes at 50 to 60 C.

The amount of reducing agent employed in the first stage may be varied over wide limits, up to 100% or more on the weight of the wool, with no appreciable effect on the properties of the modified wool produced. In general, 1% to 5% of the reducing agent on the weight of the wool will give an effective stripping action. Larger amounts may be present in the reaction mixture without significant adverse effect on the quality of the stripped product.

In the second stage the amount of reducing agent may be varied over wide limits, up to about 25% on the Weight of the wool with no significant effect on the properties of the Wool product. In general, as little as about 1% will give an effective stripping action and no advantage is gained by using more than about 5%. With colors which are difficult to strip, it is advantageous to add the reducing agent in increments at the boil, in either stage, since maximum reducing power for stripping purposes is thus utilized.

Suitable alkylating agents for use in the first stage of our process are the alkylene dihalides and substituted and modified alkylene diha-lides, for example, methylene dibromide, methylene diiodide, methylene bromoiodide, ethylene dibromide, ethylene dichloride, ethylene chlorobromide, trimethylene dibromide, 1,4-dibromobutane, 1,4-dichloro-2-butene, 2,2'-dichlorodiethyl ether, dfy-chloromethyl diphenyl and 2,2-dibromodiethyl ether. The term alkylene clihalide as used herein includes substituted and modified a-lkylene dihalides.

Very little alkylating agent is required; as little as 0.00045 mol of alkylating agent per gram of wool gives good results. Larger amounts have no deleterious eifect.

It has been found desirable to maintain the pH of the bath at 7 or above and preferably at pI-I 8-10 during the first stage treatment in the presence of the alkylene dihalide. Adjustment of the pH to the value desired can be made, for example, with allzaline salts such as borate or phosphate buffer or with borax.

Our first stage treatment so stabilizes the wool that the pH during the second-stage treatment may be lower than in the second stage and need not be alkaline but may be acid. Thus our process provides a Wide latitude in the choice of the stripping conditions and reagents employed in the second stage. Preferably, the pH during the second stage is in the range pH 3 to pH 7, as the most effective stripping action is obtained in this.

range.

The liquor-wool ratio may be varied over a wide range with no significant differences in the properties of the wool derivative formed. We prefer to employ liquor-wool ratios between about 10 to l and 40 to l.

The process is operative and most effective at temperatures between about C. and C'., although higher temperatures and temperatures as low as 60 C. may be used. Different temperatures may housed in the various stages-, The pretreatment with the oxalic and sulfuric acid bath is conveniently carried out at the boil. Although the time and temperature are not critical, it is unnecessary to prolong the treatment unduly. In general, to 30 minutes of treatment at or near the boil is conveniently carried out and easily controlled.

The duration of the first and second stages may be varied considerably. After the desired modification of the keratinous material has occurred during the first Stage, further treatment will not significantly change the properties of the modified keratin product. In general, treatment in the first stage for about one-half hour to one hour at 80 C. or from about one-quarter to one hour at 90-95 C., or at the boil gives good results. In the second stage, 10 to 20 minutes at temperatures in the range 60 C. to 100 C. has been found to be most effective and eficient, but times as short as 5 minutes or as long as 60 minutes can be used.

With the proper amount of alkylating agent present, the number of stabilized linkages that can be formed in the fiber during the first stage treatment will depend on the concentration of reducing agent, the pH of the solution and the temperature and duration of the treatment. The keratinous products treated in accordance with the present invention exhibit significantly enhanced resistance to deterioration when exposed to oxidizing, reducing, acid or alkaline agents. At the same time the mechanical properties of the W001 remain substantially unimpaired and are comparable to those of untreated wool, and the color, particularly with chrome-dyed stocks, can be stripped to a lighter shade than can be obtained with prior processes. Resistance to alkali as measured by the alkali solubility test (Brown, A. E. and Harris, M., Ind. Eng. Chem. 40, 316-22 (1948)) is markedly improved. For example, untreated wool which has an alkali solubility of 10.5% has an alkali solubility of 8.5% after passing through the entire process. Improved stability to alkali is thus demonstrated. Desirable mechanical properties, as indicated by determination of the tensile strength, are obtained and, in general, less than 10% of a drop in strength is obtained compared to that of the original wool used. Thus, by the process of this invention, not only is color stripped from the wool, but the wool is well stabilized.

It has been proposed to treat keratin with a reducing agent and subsequently to treat the re sulting product with an alkylating agent. This treatment, however, results in a product essentially different from and markedly inferior to that obtained by our invention, when the same reducing agents are used. In this sequential process, deterioration of the fiber produced by the reducing agent persists in the final product to a substantial extent. Subsequent treatment with an alkylating agent cannot restore to the keratin its original properties.

While our invention is not limited to any theory of operation, it is suggested that the alkylating agent in the reducing solution, by forming stable linkages immediately upon rupture of the disulfide linkages, preserves the physical properties of the material.

When unmodified keratinous material is treated with reducin agent alone, under the conditions of our treatment, a substantial number of sulfhydryl groups is formed, as indicated by a strong nitro-prusside reaction. The mechanical properties of wool so treated are markedly inierior to those of the untreated productits tensile strength is greatly weakened and a fabric so treated becomes stiff and boardy. In our process, however, these detrimental efiects noted with reducing agent alone are negligible.

Our process is capable of easy control. It is relatively insensitive to small variations in conditions such as concentration of reagents, time of treatment, etc. No damage is caused either by high concentrations of reducing agent orby unduly prolonged treatment. Since it is known that various reducing agents, dependent upon the conditions under which they exert maximum stripping efiiciency, destroy dyestuffs by difierent routes such that different colorations are produced, our invention provides the possibility of obtaining a new range of shades in stripped wools, by selection of various combinations of different stripping agents and different stripping conditions for use in the two stages.

In all of the above examples, using a wide variety of chrome dyestuffs, it was found that the color of the stripped stock was of a lighter shade than could be produced if the treatment with oxalic and sulfuric acid were omitted. This is indeed a surprising result. We believe, although we do not wish to be limited by any theory, that the acidic oxalic acid treatment loosens the combination between wool and dyestuff so that the dyestuff is more susceptible to removal by the subsequent treatments which are mentioned in the examples.

This theory is supported by some interesting evidence. For example, when chrome dyed wool is treated with the bath containing oxalic acid and sulfuric acid little or no chromium is removed and little or no color is removed. When chrome dyed wool is treated by the processes of U. 3. Patent No. 2,508,714 or by our process omitting the pretreatment step, generally less than 20% of the chromium is removed. However, with the processes of the examples, 80 to 90% of the chromium on the wool is removed, and much superior stripping is obtained in all cases. In every case, the pretreatment With oxalic acid and sulfuric acid facilitates subsequent removal of chromium and this is desirable inasmuch as residual chromium on stripped stock may interfere with shades produced on redyeing.

While it may appear from these results that chromium removal and stripping of color are directly related, this is not always so. For example, with some chrome dyestuffs desirable stripping is obtained by our processes in which the pretreatment step is omitted without sublieved that our pretreatment with oxalic acid and sulfuric acid, through formation of complexes, facilitates removal of dyestuff along with that of metal, and this is advantageous.

The process of this invention employing the pretreatment step strips acid dyestuffs and other wool dyes as Well as does our process in which the pretreatment step is omitted. Thus, in stripping normal commercial mixtures where dyed Wools of all types are present the process of this invention employing thepretreatment step provides the advantage that not only are the acid dyestuffs readily removed but the chrome dyestuffs are also removed better than by any previous process.

The order of the steps in the process of this invention is important. If the treatment with oxalic and sulfuric acids is interposed between the treatment with hydrosulfite and alkylene dibromide and the subsequent treatment with re- 9. ducing agent no improved result is obtained. No improved result is obtained if the oxalic and sulfuric acid step is used after the final treatment with reducing agent. It is important that the oxalic and sulfuric acid treatment be used before the hyd-rosulfite-alkylene dibromide step.

Since the use of chrome dyestuffs on wool has increased in recent years, the process of this invention employing thepretreatment step becomes very useful in stripping such materials better than previously available methods. Similarly the olive drab shades found in Army goods are also largely produced by chrome dyeing, and by this invention, such materials are stripped'to light desirable shades.

The present application is a continuation-inpart of our prior application Serial No. 160,582, filed May 6, 1950 now abandoned, which is a continuation-in-part of our prior Patent No. 2,508,714.

We claim:

1. The process for stripping color from a keratinous material while increasing its resistance to attack by oxidizing agents, reducing agents, acids and alkalis and preserving substantially unimpaired its mechanical properties, which comprises treating the keratinous material at a temperature above 60 C. and a pI-I above 7, in a liquid bath containing 1% to 100% of the weight of the keratinous material of a reducing agent for keratin selected from the class consisting of sulfoxylate formaldehyde compounds, hydrosulfites and formamidine sulfinic acid, to rupture disulfide cross linkages of the keratinous material and strip color therefrom, said bath also containing more than 0.000425 mol per gram of keratinous material of an alkylene dihalide, whereby new stable alkylene cross linkages between the peptide chains of the keratin are formed immediately upon rupture of the disulfide linkages, and thereafter treating the keratinous material at a temperature above 60 C. and a pH of 3 to 7 in a liquid bath containing 1% to 25% of the weight of the keratinous material of a reducing agent selected from the class consisting of zinc hydrosulfite and a mixture of zinc sulfoxylate formaldehyde and an acid for stripping oolor from the keratinous material.

2. The process of claim 1 wherein the material to be treated is a chrome-dyed keratinous material and the stripping treatment is preceded by treatment or" the keratinous material for from to 30 minutes at the boil in acidified aqueous solution at pll of 1.5 to 2.5 of 1%l0% on the weight of the keratinous material of oxalic acid.

3. The process for stripping color from a heratinous material while increasing its resistance to attack by oxidizing agents, reducing agents, acids and alkalis and preserving substantially unimpaired its mechanical properties, which comprises treating the keratinous material at a temperature above 5Q" C. and a pH above 7, in a liquid bath containing 1% to 10% of the weight of the keratinous material of sodium hydrosulfite to rupture disulfide cross linkages of the keratinons material and strip color therefrom, said bath also containing more than 3.00045 mol per gram or keratinous material of ethylene dibromide, whereby new stable alkylene cross linkages between the peptide chains of the keratin are formed immediately upon rupture of the disulfide linkages, and thereafter treating the keratinous material at a temperature above 60 C. and a pH of 3 to '2 in a liquid bath containing 1% to 25% of the weight of the keratinous mate- 10 rial of a reducing agent selected from the class consisting of zinc hydrosulfite and a mixture of zinc sulfoxylate formaldehyde and an acid for stripping color from the keratinous material.

4. The process of claim 3 wherein the material to be treated is a chrome-dyedkeratinous material and the stripping treatment is preceded by treatment of the keratinous material for from 5 to 30 minutes at the boil in an acidified aqueous solution at pH of 1.5 to 2.5 of 1%-l0% on the Weight of the keratinous material of oxalic acid. .7 i

5. The process for stripping color from a keratincus material while increasin its resistance to attack by oxidizing agents, reducing agents, acids and alkal-is and preserving substantially unimpaired its mechanical properties, which comprises treating the keratinous material at a temperature above 60 C. and a pH above '7, in a liquid bath containing 1% to of the weight or" the keratinous material of a reducing agent for keratin which is inert to alkylene dihalides, to rupture disulfide cross linkage of the keratinous material and strip color therefrom, said bath also containing more than 0.00045 mol per gram or keratinous material of an alkylene dihalide, whereby new stable alkylene cross linkages between the peptide chains of the keratin are formed immediately upon rupture of the disuliide linkages, and thereafter treating the keratinous material at a temperature above 60 C. and a pH of 3 to 7 in a liquid bath containing 1% to 25% of the weight of the keratinous material of a different reducing agent selected from the class consisting of zinc hydrosulfite and a mixture of zinc sulfoxylate formaldehyde and an acid. Y

6. The process of claim 5 wherein the material to be treated is a chrome-dyed keratinous material and the stripping treatment is preceded by treatment of the keratinous material for from 5 to 30 minutes at the boil in an acidified aqueous solution at pH of 1.5 to 2.5 of 1%-10% on the weight of the keratinous material of oxalic acid.

'7. The process for stripping color from dyed wool while increasing its resistance to attack by oxidizing agents, reducing agents, acids and alkalis and preserving substantially unimpaired its mechanical properties, which comprises treating the wool at a temperature above 60 C. and a pH between 8 and 10 in a liquid bath containing 1% to 100% of the weight of the wool of sodium hydrosulfite to rupture disulfide cross linkages of the wool and strip color from the wool, said bath also containing more than 0.00045 mol per gram of wool of ethylene dibromide, whereby new stable alkylene cross linkages between the peptide chains of the keratin of the wool are formed immediately upon rupture of the disulfide linkages, and thereafter treating the wool at a temperature above 60 C. and a pH of 3 to '7 in a liquid bath containing 1 to 5% of the weight of the wool of zinc hydrosulnte.

8. The process of claim 7 wherein the wool is I a chrome-dyed wool and the stripping treatment is preceded by treatment of the wool for from 5 to 30 minutes at the boil in an acidified aqueous solution at pH of 1.5 to 2.5 of 1%-10% on the weight of the wool of oxalic acid.

9. The process for stripping color from dyed wool while increasing its resistance to attack by oxidizing agents, reducing agents, acids and alkalis and preserving substantially unimpaired its mechanical properties, which comprises treating the wool at a temperature above 60 C. and a pH between 8 and 10 in a liquid bath containing 1% to 100% of the weight of the wool of sodium hydrosulfite to rupture disulfide cross linkages of the wool and strip color from the wool, said bath also contaning more than 0.00045 mol per gram of wool of ethylene dibromide, whereby new stable alkylene cross linkages between the peptide chains of the keratin of the wool are formed immediately upon rupture of the disulfide linkages, and thereafter treating the wool at a temperature above 60 C. and a pH of 3 to 7 in a liquid bath containing 1 to 5% of the Weight of the wool of a mixture of zinc sulfoxylate formaldehyde and an acid.

10. The process of claim 9 wherein the wool is a chrome-dyed wool and the stripping treatment is preceded by treatment of the wool for from 5 to 30 minutes at the boil in an acidified aqueous solution at pH of 1.5 to 2.5 of 1%-10% 0 on the weight of the keratinous material of oxalic acid.

12 References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 837,730 Reinking Dec. 4, 1906' 1,524,737 Kritchevsky Feb, 3, 1925 1,594,670 Hollander Aug. 3, 1926 1,696,164 Hollander Dec. 18, 1928 1,935,217 Ulrich Nov. 14,1933 1,958,483 Loughlin May 15, 1934 2,508,714 Harris et al May 23, 1950 OTHER REFERENCES Gaunt: Some Recent Observations on the Theory of the Dyeing of W001 with Chrome Dyes, J. Soc. Dyers and Colourists, September 1949, vol. 65, No. 9,- pp. 429-433, p. 429 esp. pertinent. I

Race et al.: Nature of the Dye-Chromium- Fibre Complex in the Case of Wool Dyed with Certain Chrome Mordant Dyes, J. Soc. Dyers and Colourists, December 1946, pp. 372-381. 

1. THE PROCESS FOR STRIPPING COLOR FROM A KERATINOUS MATERIAL WHILE INCREASING ITS RESISTANCE TO ATTACH BY OXIDIZING AGENTS, REDUCING AGENTS, ACIDS AND ALKALIS AND PRESERVING SUBSTANTIALLY UNIMPAIRED ITS MECHANICAL PROPERTIES, WHICH COMPRISES TREATING THE KERATINOUS MATERIAL AT A TEMPERATURE ABOVE 60* C. AND A PH ABOVE 7, IN A LIQUID BATH CONTAINING 1% TO 100% OF THE WEIGHT OF THE KERATINOUS MATERIAL OF A REDUCING AGENT FOR KERATIN SELECTED FROM THE CLASS CONSISTING OF SULFOXYLATE FORMALDEHYDE COMPOUNDS, HYDROSULFITES AND FORMAMIDINE SULFINIC ACID, TO RUPTURE DISULFIDE CROSS LINKAGES OF THE KERATINOUS MATERIAL AND STRIP COLOR THEREFROM, SAID BATH ALSO CONTAINING MORE THAN 0.00045 MOL PER GRAM OF KERATINOUS MATERIAL OF AN ALKYLENE DIHALIDE, WHEREBY NEW STABLE ALKYLENE CROSS LINKAGES BETWEEN THE PEPTIDE CHAINS OF THE KERATIN ARE FORMED IMMEDIATELY UPON RUPTURE OF THE DISULFATE LINKAGES, AND THEREAFTER TREATING THE KERATINOUS MATERIAL AT A TEMPERATURE ABOVE 60* C. AND A PH OF 3 TO 7 IN A LIQUID BATH CONTAINING 1% TO 25% OF THE WEIGHT OF THE KERATINOUS MATERIAL OF A REDUCING AGENT SELECTED FROM THE CLASS CONSISTING OF ZINC HYDROSULFITE AND A MIXTURE OF ZINC SULFOXYLATE FORMALDEHYDE AND AN ACID FOR SRIPPING COLOR FROM THE KERATINOUS MATERIAL. 